Liquid seal



June 2.6, 1956 J. A. LIGGETT 2,751,926

LIQUID SEAL Filed March 2o, 195s Ig 4 j? j f4 /I TTOR NE Y United States Patent` Oce 2,751,925 Patented June 26, 1956 LIQUID SEAL John A. Liggett, Haddonfield, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application March 20, 1953, Serial No. 343,780

6 Claims. (Cl. 137-251) The present invention is related to apparatus providing a liquid seal.

It is sometimes desired to fill an enclosed space with a fluid of gaseous form which has first been treated to exclude an undesired vapor. An example is found in the art of transmission of high frequency electromagnetic waves. The transmission lines for the waves may take the form of hollow pipe waveguides, or of coaxial lines in which the outer conductor is in the form of a pipe. The pipes are sealed from the external atmosphere, by suitable seals. The enclosed space, within the hollow pipe waveguide in the one case, or between the conductors in the other case, is to be filled with purified air, that is, air from which moisture in the form of water vapor has been excluded. The reason is that dry air affords a better dielectric with higher voltage breakdown, permitting the line to carry greater power without arcing, than when ordinary air is employed. Also, moist air may condense on cooling of the pipe, and may collect in the form of liquid at the bottom of the line, thereby causing power loss, or a short-circuit, or undesirably high reflections.

In the past, in some cases, the transmission line is filled with dry air by pressurizing the line from a tank of gas, such as nitrogen, through a pressure regulating valve, to avoid the above difficulties. In other cases, an air pump is employed, from which the air is led through a desiccant into the transmission line pipe. In some forms of apparatus, the pump is maintained in'continuou's operation, with suitable relief means in the pipe, preferably at the end. In others, vent means are provided if lthe pressure exceeds a certain amount. It has been customary to employ positive pumping means, that is, anvair pump of the piston type, even though centrifugal blowers are already available in the transmitter for Acooling purposes.

Blowers have not been used extensively because they provide only a low pressure, for which it is diic'ult to supply suitable check valve means, in order to prevent blow-back, that is, gaseous fluid feed in the reverse direction. Also, it is diiiicult to provide suitable relief means for a blower pump because of the low pumping Y pressures.

It is an object of the present invention to provide a liquid seal apparatus for an enclosed space which simultaneously affords a relief means and means for maintaining pressure inthe pipe above atmospheric pressure, even after the volume of gas or air within the pipe cyclically expands and contracts or slowly leaks out. v Another object of the invention is to provide a liqui seal device for transmission lines and the like which enables the use of a fan blower or the like for pressurizing l mit useof one or more such impositive pumps orblowers y simultaneously or intermittently.

A further object of the invention is to permit the use of a plurality of pumps, and especially impositive pumps such as blowers, either singly or concurrently or intermittently, without danger of blow-back or serious loss of the low pressure gaseous fluid and without any manual switching or mechanical valves.

A further object of the invention is to provide positive sealing affording relief on excessive expansion of gaseous fluid in the space to be lled thereby, and yet maintaining pressure, without additional pumping, when thereafter the gaseous fluid contracts and expands again slightly.

Another object of the invention is to provide positive sealing means, affording admittance of gaseous fluid to a space to be occupied thereby, only after depriving the fluid of an undesired gas or vapor, thereby to purify it, and thereafter allowing the line to breathe (affording relief on expansion and taking in the fluid on contraction), without more than the initial pressurizing, and also at the same time maintaining the purity of the liquid in the space, that is, excluding the undesired gas or vapor, and also maintaining the requisite seal of the pumps.

A -still further object is to maintain the purity of the gaseous fluid in the line at low pressure, and permit the line to be further pressurized at any time to the initial low pressure, still maintaining the fluid purity.

In a preferred and successfully used embodiment of the invention, a primary chamber is provided in which a liquid for the liquid seal is to be placed, to a normal lever when the device is not in use. The primary chamber communicates through its top with the space to be pressurized or filled with the gaseous fluid. An auxiliary chamber is provided, above the normal liquid seal level. The auxiliary chamber or reservoir has a Vent opening at its top. Communication is also afforded between the two chambers: (l) By a relief passageway between the upper portion of the auxiliary chamber and below the normal level of the sealing liquid at a first point in the primary chamber; and (2) By a passageway between the bottom of the auxiliary chamber and a second point in the primary chamber below the first point. At least one inlet passageway or tube communicates from a third point below the first point in the primary chamber to the input from one or more of the blowers or pumps to be employed, above the normal level, so that each blower or pump has its individual liquid sealed inlet passageway. In operation, assuming blowers to be employed and a suitable non-contaminating sealing liquid in the primary chamber, the gaseous liquid passes through the inlet passageways, passes through the liquid, the primary chamber, andan interposed purifying agent to the space to be pressurized, for example, a transmission line pipe. The liquid seals these inlet passageways when the blowers are not working. If the transmission line gas expands, the back-pressure raises the liquid level in the passageways communicating with the primary chamber, and in the auxiliary chamber, and thus lowers the liquid level below the first point in the primary chamber until the primary chamber is vented through the uncovered relief passageway, and through the auxiliary chamber. The other primary chamber communicating passageways thus remain sealed, since the primary chamber liquid level cannot go lower than the opening of the relief passageway at the first point.

The foregoing and other objects, advantages, and novel features of the invention will be more fully apparent from the accompanying drawing, the sole figure of which is a cross-sectional view taken in a central vertical plane, of a preferred embodiment of the invention, actually employed for pressurizing transmission lines with dried air.

Referring to the drawing, a primary chamber 10 is enclosed by a cylindrical side wall 12, a base 14, and a top before the venting action begins.

1'5. The base 14 vis 'provided with a drainage valve 18. The side wall 1.2 has a. sealed viewing window L20 .for inspection of the liquid level. A reservoir or auxiliary chamber 22 is sealed to and suspended from the top 16, by having the Vupper end of ya cylindrical-side wall 24 Vseated in-a cylindrical `inset of top ld and hermetically sealed thereto, ycoaxially'with the primary chamber side wall 12. At its top, the Vauxiliary chamber 22 communicates with outer air through the transversely drilled vent opening 25 in the top 16. The auxiliary chamber .22 has a bottom 26 drilled to receive a relief tube 28 and .reservoir drain tube 3). The bottom open Iend of .the relief tube 28 is at'the lowest Aexpected liquid level and .isabove the bottom open end of the reservoir drain tube 30. The relief tube 28 is hermeticallysealed to the auxiliary chamber 'bottom 26 and passes through the latter and up into the auxiliary chamber, and has a side opening 32 substantially at vthe top of the auxiliary chamber. This side opening .faces away from the reservoirchamber opening 25 for lapuipose which will appear. The upper end of the reservoir `tube 30 is hermetically sealed to the auxiliary chamber bottom 26 at the bore drilled to receive it.

An inlet tube 34 has .its bottom open terminated Vin primary chamber below the lower opcn end of relief tube 28, but above the lower open end of pressure tube 30. At Vits upper open end the inlet tube 34 "is hermetically vsealed into a bore 36 extending vertically into the primary chamber top 16 to meet and communicate with a transverse bore 38 from the side of the primary chamber top 16. VA threaded nipple V4t) is sealed to the transverse bore 38 to .provide easy connection to the rtubing from a blower or the like (indicated butV not shown). Other inlets such as `nipple 40, bores 38, 36, and inlet tube 34 are indicated by showing only a second tube 34', the construction being similar.

In the embodiment illustrated, due to surface tension,

Y the level ofthe liquid actually goes about lx inch, for

example, below the bottom opening of relief tube 28 Therefore the bottom 'of reservoir drain tube 30 is suciently below (i716 inch, for example) the lower end of relief'tube 28, so thatno critical dimensions are involved. These dimensions are Y by Away of example. On the other hand, tubes 34 should "only be 'a distance below the liquid level 72 such .that .the pressure available from the Yblowers in inlet tube .34 'readilyovercomes Va head of theliquid equal to thatdistance. As it is here desired to operate at quite low pressures ininlet tube'3'4 'from the blower, the lower openingof the inlet Vtube 34 is intermediate the l.lower openings 'of 'the 'other "two Vtubes '28 and '30.

An outlet Vaperture 42 is drilled vertically (axially) in the primary 'chamber top i6. The top 16 has a depres- 'sion'in which is 'removablyseated a cylindrical container 44 havinga glass 'or Vtransparent plastic cylindrical side Wall 46. A perforated'shelf 4S rests on a retaining ring 56 cemented to the .glass wall '46 near or at the lower end of'container 44.. On the perforated shelf 48 rests a porous feltpad 5'1. A desiccant 52 such as silica gel or calcitun sulphate (CaSO4) treated in a known manner with an agent to change color 'on the acquisition of moisture to an amount to .reduce'its eicacy, Ais placed in the container 44. The 'desiccant 52 may thusbe inspected fdr its elicacy through glass wall 46. A 'lid "54 has a rimto fit 'snugly around the top of the glass cylinder '46, 'and equally 'spaced circumferentially three radially `extending ears 56 which clear 'the rim. VThe top 16 has three equally circumferentially spaced slotted VYe'ars :58 Vof which the bottom of rods 6() are pinned, as

shown. The rodslare thus free to swing clear of container 414, when disengaged, 'but are retainedby therpins 'to withstand tension. At their tops, the rods are -threaded enlarged heads Vto hold them 'at the earsx56. Neoprene,

- mounted with vertical cylindrical axes.

gaskets 64 and 66 at top and bottom respectively of the glass wall 46 prov-ide a .seal between the lid .54 .and .the upper rim of the glass wall, and between the top 16 and the lower rim of the glass wall, respectively, when the thumb screws 62 are tightened in the rods, thus hermetically sealing the container 44 from the outer atmosphere.

In the lid 54 are two (any plurality may be provided) apertures 68. A right angle pipe fitting 'i0 is provided for each aperture and hermetically sealed to the lid 54.

Each pipe fitting 70 has an outward facing threaded nipple for ready attachment to'pipes :leading 'to .the transmission -line pipe to be pressurized.

To Vplace -the .apparatus illustrated in operation, it is The three thumb screws 62 are loosened and the irods Y`6i! swung down. The container 44 is removed. Using a small funnel or the like, a nou-contaminating liquid, for example, in this case, ethylene glycol, is poured into the outlet aperture 42. By Irion-contaminating liquid is simply vlfmeant one which has no vapor which will contaminate the .gaseous uid with undesired "-vapor. `ln the present case, water would be Ya contaminating vapor. The proper Vnormal level -of @liquid is indicated 4by 'the dotted 'line at 7.2 to

f cover the @op'en `bottomof .relief tube 28. The dimensions thumb screws tightened to provide a Igood seal 4at the gaskets 64, 66. The glass wall of container 44 allows inspection :of the color `of thexdesiccant 52 -to determine if yit isin a state lto absorb further :water vapor, or if the desiccant should be freplaced.

A suitable tubing :,(vrrot shown), -as ofcopper, may now b'e run from eachiblower to .each inlet nipple 40. .-lf rdesired, :but not necessarily, `rthe inlet nipples 40 rnot used mafy be closed. .A exible tubing (not shown) may be inserted .between the blower and :the copper Ytubing `to prevent vibration transmission `from the blowers to the n device shown.

Copper "tubing may -be yinstalled bet-Ween the `outlet ttings .70 and the transmission .lines which are to be lle'd with dry air. .As this .particular equipment is designed `for use at .a .microwave .relay .transmitting andreceiving station lto supply-dry airto the transmission lines `from the .transmitter and .receiver to `the antennas, the outlets -are =indicated Yas .leading tto .antenna lines. The transmission line is generally hermetically sealed from .the .outer atmosphere, .and the tubing :should join at theffitting 7D man airtight manner .as well. It is an advantage of 'the present sealing device that slow leaks in thesystem-transmission lines .can be tolerated, because the Atransmitter-.receiver station is in'operation virtually continuously, withoneblower nearlyvalways forcing .puried air into the system. Therefore, the supply of air forced through 'the :system ,is substantiallycontinuous,

without any additional equipment, except .for the inex-Y pensive liquidseal device .,itself, being required. flf .only

"one outlet iittin'g 70 lisused, the other must be capped (not shown-) `'or-"otherwise sealed. lf .more than ftwo :outlets are desircdfa suitable'Tjunction (not shown) :maybe inserted where-convenient.

"The 7tubing fromthe iblower, may now -be connected to -the flexible vtubing 1mentioned above, "and ftested -`for air ow. The free end of the hose may be dipped about a half 'inch 'under ethylene 'glycol in a bottle or pail.

If "bubbles 'rise "freely, the -pressure is 'suic'ienh TheV Y v'free end is then 'connectedl'to the in'le't 'nipple 40. 1f

more 'than -one "'brower vrs used'tlre same test may be l avancee employed for the second blower before connection to the other inlet copper tubing and nipple 40.

The air from the blower, as noted, may be under small pressure, say equivalent to a head of one inch of ethylene glycol. Now a release valve or bleeder valve (not shown) at the end or ends of the transmission line or lines remote from the outlets 70 is opened, and the blower turned on, to bleed the transmission lines. This bleeding is to remove any moist air initially in the lines.

It is apparent that during the bleeding operation air from the blowers will be forced into the inlet tube 34, bubble through the liquid, ethylene glycol, and increase pressure in the primary chamber 10. The liquid level in the chamber will be forced down from the level 72, and up in the relief tube 28 and the auxiliary chamber tube 34). However, the open bottom of the relief tube 28 remains sealed, because only a slight pressure is required to cause the air to flow from the primary chamber through the outlet aperture 42, the perforated shelf 4S and porous pad 51, and the desiccant 52. After drying by the desiccant, the decontaminated or purified air, with water vapor removed, ows through the outlet fittings toward the bleeder openings at the ends of the transmission lines. After the transmission lines or other space to be filled with dry air has been thus bled of moist air and completely lled with dry air, the bleeder openings at the transmission line ends may be closed or sealed.

Air cannot at any time ow out the inlet tubes 34 which are unconnected or connected to idle blowers because the liquid will rise in these tubes to a level such as 74 equal to the equivalent pressure in the primary chamber 10.

If all blowers are idle, the liquid in all tubes will rise to a level such as 74 and pressure will be maintained in the primary chamber and the transmission line. Due to temperature increase, the volume of air in the transmission line may expand and the pressure in the transmission line may increase. Relief is afforded for excessive pressure without forcing liquid out through inlet tubes 34. Increased pressure at the ttings 70 causes increased pressure in the primary chamber 10. This causes the liquid level in the tubes and in the auxiliary chamber to rise to a level such as 76. Due to the capacity of the reservoir or auxiliary chamber 22, the liquid level in the primary chamber 10 drops to the bottom of relief tube 28. Without this auxiliary chamber 22 the liquid raised in the tubes might not be suicient to adequately lower the level in the primary chamber it?. When the liquid level is slightly below the bottom of relief tube 28, the air from primary chamber 10 clears liquid from relief tube 28 into the auxiliary chamber 22, where it is collected with the liquid in the auxiliary chamber 22. The relief tube upper opening is faced as described, because by facing this opening away from the reservoir chamber vent opening 25 no liquid can be lost as a result of spatter over opening 25. The air is then relieved from primary chamber 10 through the relief tube 2S and the vent opening 25. When pressure is thus relieved, liquid ilows from the auxiliary chamber 22 back into primary chamber 10 through the reservoir drain tube 3i). lf one or more blowers alord an excessive pressure at inlets 40 and inlet tubes 34 the air will be similarly relieved from chamber 10 through relief tube 23 without breaking the seal in any of the other inlet tubes 34.

With all blowers olf or no connections to the inlet tubes at nipples 40, the device illustrated maintains pressure in the airtight transmission lines at a given or increasing temperature.

When the transmission line fluid contracts, the liquid from the reservoir and pressurizing passageway, as well as from the other passageways, returns to the primary chamber, and by the hydrostatic head exerted by the 6 l liquid, maintains the transmission line pressure through the passageway to the transmission line.

Thus the transmission line breathes, but always with a pressure maintained in it when any one or all blowers are operative. When all blowers are inoperative, the line breathes in the same manner and pressure will usually be maintained. As the transmission line breathes, it does so through the purifying agent 52, and therefore, the desired purity of the transmission line is maintained.

lf the temperature of the transmission line cycles, that is, goes successively up and down, the air from the trans mission line continually passes out or in through the desiccant, and air never enters the transmission lines unless passing through the desiccant. Moreover, as the temperature cycles, the system reestablishes a pressure above external pressure in the transmission lines with each cycle, even though the cycles become progressively lower in average temperature.

It is an especial advantage to have available a system operative on such low pressures as alforded by the device illustrated. Blowers are usually available in and part of the system of a transmitter station for cooling purposes. Merely funnelling the air from the blower affords a pressure at the inlet sufficient for operating the equipment, and without affecting the circulation of cooling air, if this air is funnelled from the appropriate point. Pressure in the transmission line or space to be lilled with the gaseous fluid (air) is never greatly different from ambient air pressures. This is advantageous because no extreme precautions are necessary to provide seals suiicient to withstand such small pressure differentials.

it will be apparent that the invention thus disclosed comprises a device which affords a liquid seal for a space to be lled with a puriiied gaseous iluid. One or more impositive low pressure pumps may be operated simultaneously, singly, or intermittently, without manual switching or mechanical valving to relieve excessive back pressure. The liquid seal afforded by the device of the invention is sure and substantially failure proof, and requires little maintenance.

What is claimed is:

l. In an arrangement for delivering gas under pressure to a space to be iilled with gas, in combination, a closed container adapted to be partially filled with a liquid to a given level; first tubular means adapted to be connected at one end to a source of gas under pressure and extending at its free end into said container to a point below said given level; an air reservoir formed with an opening to the atmosphere; second tubular means communicating with said air reservoir and container extending from the lower portion of said air reservoir, when the latter is in operative position above said given level, to a point in said container below the free end of said rst tubular means, third tubular means communicating with said air reservoir and container extending from the upper portion of said reservoir, when the latter is in said operative position, to a point in said container below said given level but above said free end of said rst tubular means; and outlet means including a passageway through the wall of said container at the upper portion of said container adapted to communicate with said space to be filled with gas.

2. ln an arrangement as set forth in claim l, said air reservoir being located within said container and said opening to the atmosphere including a passageway extending from said air reservoir through a wall of said container.

3. In an arrangement for delivering gas under pressure to a space to be filled with gas, in combination, iirst and second container means which, in operative position, are mounted one above the other and together are closed from the atmosphere, said two container means being provided with a passageway for permitting gas to move from one container means to the other, said lower container means being adapted to be partially lled with a liquid to a given level, when in operative position; rst tubular means adapted to be connected at one end to-a source of pressurized gas and extending 'at its Vfree 'end into the lower container means to arpointbel'ow said given level; 'an air reservoir formed with an 'opening'to the atmosphere; second tubular means communicating with Vsaid Vlower container 'means and said air reservoir extending from the lower portion of said air reservoir, when the latter is in operativerposition above said given leve1,`to 'a point in said lower container means below said free end of said rst tubular means; third tubular means communicating with said lowercontainer means and said air reservoir extending fromithe upper portion'of said reservoir, when the latteris in said operative position', to a point in said lower container-means below said Vgiven level but above said free end of said 'rst ftubular means; a purifying agent located in saidfupper container lmeans yfor-purifying the gas passing vfrom said lower container means through said upper containenmeans; and-outlet-'means mounted on a Wall of said upper container means andopening into said upper container means, and adapted to Vcommunicate with said space to be vfilled with gas.

4. in .anarrang'ement as `claimed inclaim 3, said purifying agent Vcomprising a desiccant.

5. .In 'an arrangement as set forth in claim 4, said air reservoir'beinglocated lin said lower container means and being vcompletely closed Voff therefrom except at thefree ends of the secondA and' third tubular means,V and said lower container means being formed with a passageway in a tainer to a given level; a rst tubular member adapted to be connecteda't one .'endto'a sourceof'pressurized'gas and.Y

extending at itstfree-'end into the lower container to a'point below said given llevel; an air reservoir ,closed from said lower vcontainer 'an'dmounted above'said given level to an Y upper 4wafll'of saidlowercontainer, said 'upper Wall of said lower 'container beingpfou-ned with va passageway opening intro said air vreservoir and extending tothe outer atmosphere; second ytubular means communicating v-with said lower container and air reservoir extending lfrom vthe'Y said given level but above said'free endof said first tubular wall thereof extending from .the upper portion of said air reservoir, when the latter is in said operative position, to

v form said opening Yto the atmosphere.

means; a desiccating agent substantially -illing the upper container lfor A'drying the gas vpassing Vfrom said flower container thronghsaid'upp'er container; fand outlet means located Vin the .uppenporti'on .of said `upper container, when Y the latter isV in operative position, opening at one end into f said upper :container Iand :adapted to Vcommunicate with the'spaceltotbe lled :withfgasl References -Gitediin the file of lthis patent UNITED STATES PATENTS 

